This project investigates the development and function of mononuclear phagocytes in various pathologic conditions, using combined electron microscopic and cytochemical techniques. Work now in progress consists of investigating the subcellular distribution of lysosomal enzymes and peroxidase in BCG stimulated alveolar macrophages and in the epithelioid and giant cells of chronic granulomata. BIBLIOGRAPHIC REFERENCES: Morris, Robert B., Nichols, Barbara A., and Bainton, Dorothy F.: 1975, Ultrastructure and peroxidase cytochemistry of normal human leukocytes at birth. Dev. Biol. 44:223-238. Bainton, D.F., Nichols, B.A. and Farquhar, M.G.: 1976, The primary lysosomes of blood leukocytes. In: Lysosomes in Biology and Pathology, Vol. 5, Eds. J.T. Dingle and R. Dean, North-Holland Publishing Co., Amsterdam and London. (In press).